package com.chen.rw;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * 读写锁
 * 独占锁（写锁） 一次只能被一个线程占有
 * 共享锁（读锁） 多个线程可以同时占有
 * ReadWriteLock
 * 读-读 可以共存！
 * 读-写 不能共存！
 * 写-写 不能共存！
 */
public class ReadWriteLockTest {
    public static void main(String[] args) {

        MyCacheLock myCacheLock = new MyCacheLock();

        // 写入
        for (int i = 1; i <= 5; i++) {
            final int tempI = i;
            new Thread(() -> {
                myCacheLock.put(tempI + "", tempI);
            }, String.valueOf(tempI)).start();
        }

        // 读取
        for (int i = 1; i <= 5; i++) {
            final int tempI = i;
            new Thread(() -> {
                myCacheLock.get(tempI + "");
            }, String.valueOf(tempI)).start();
        }

    }
}

// 自定义加锁的缓存
class MyCacheLock {
    private volatile Map<String, Object> map = new HashMap<>();
    // 读写锁更加细粒度的控制
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    // 写。写入的时候希望只有一个线程写
    public void put (String key, Object value) {
        // 写锁加锁
        readWriteLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "写入" + key);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "写入OK");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 写锁释放锁
            readWriteLock.writeLock().unlock();
        }
    }

    // 读。所有线程可以同时读
    public void get (String key) {
        // 读锁加锁
        readWriteLock.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "读取" + key);
            map.get(key);
            System.out.println(Thread.currentThread().getName() + "读取OK");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 读锁释放锁
            readWriteLock.readLock().unlock();
        }
    }
}
